This message came from the CF Trac system. Do not reply. Instead, enter your
comments in the CF Trac system at http://cf-trac.llnl.gov/trac/.
#118: Add an attribute in Appendix F to identify the geoid
-----------------------------+------------------------------
Reporter: jonathan | Owner: cf-conventions@…
Type: enhancement | Status: new
Priority: medium | Milestone:
Component: cf-conventions | Version:
Resolution: | Keywords:
-----------------------------+------------------------------
Comment (by rsignell):
Jonathan, I'm dragging my feet here because now I'm a bit confused about
the utility of this ticket. I originally supported this because I thought
this would be a way to specify heights relative to a gravity-based datum.
I had not realized that ticket http://cf-trac.llnl.gov/trac/ticket/69
allowed the specification of the vertical coordinate system via
```VERT_CS```, which is why I thought I was supporting ''this'' ticket.
Everyone who does river, lake or ocean modeling uses heights relative to a
orthometric (gravity-based) datum (so that water flows down hill!), and
folks in the US use NAVD88 (they used to use NGVD29). Neither of these
are geoides, but they are intended to be gravity-based datums. So we
need a way to say that our heights are in meters relative to NAVD88 or
NGVD29, not relative to a GEOID.
This ticket allows for the geoid model to be identified (e.g. GEOID12B),
but not for way to specify the vertical datum.
The CF Standard Name currently defines altitude as "Altitude is the
(geometric) height above the geoid, which is the reference geopotential
surface. The geoid is similar to mean sea level."
But perhaps we should define altitude as "Alitude is height above an
orthometric (gravity-based) datum" and redefine this ticket to define a
"vertical_datum", where NAVD88 would be one of the possible values (along
with other gravity-based datums).
The very term geoid is a bit fuzzy, apparently:
http://www.ngs.noaa.gov/GEOID/geoid_def.html
Perhaps we should just provide a way to specify vertical datums that are
commonly understood and used.
And in the meantime, I'll start using the ```crs_wkt``, since that will
solve my problem immediately!
--
Ticket URL: <http://cf-trac.llnl.gov/trac/ticket/118#comment:11>
CF Metadata <http://cf-convention.github.io/>
CF Metadata
This message came from the CF Trac system. To unsubscribe, without
unsubscribing to the regular cf-metadata list, send a message to
"majord...@lists.llnl.gov" with "unsubscribe cf-metadata" in the body of your
message.
